Hand-held signals (HHS) are devices generally used for illumination to signal troop movements, and in attracting the attention of aircraft crews. More specifically, such devices are used both day and night, to provide a beacon for rescuers, or to disclose, or illuminate the positions of military units or personnel. Such rescue or attention getting applications are common in non-military situations, as well as, in military combat and training scenarios. Generally, HHS formulations contain significant amounts of potassium perchlorate (KClO4), a strong oxidizing material—which exothermically transfers oxygen to combustible materials, to provide pyrotechnics with a significant rate of combustion in air. However, KClO4 contaminates groundwater and impacts public drinking water. KClO4 interferes with hormonal regulation of the thyroid gland, and is known to be teratogenic. Accordingly, the US Environmental Protection Agency has established a permissible KClO4 level at 15 parts per billion, and various states have mandated even lower levels, e.g. California has mandated no more that 6 parts per billion and Massachusetts has mandated only 2 parts per billion. In response, the US Department of Defense is spending billions of dollars annually on perchlorate remediation efforts.
Colors in pyrotechnics are obtained by the addition of specific ingredients, which offer the desired flame color. For example, green is obtained with the addition of barium nitrate, which acts as both a color agent and an oxidizer. Similarly, strontium nitrate provides intense red and also acts as an oxidizer. The corresponding light emitting species (in the gas phase, during flaming) are the monohydroxides, SrOH and BaOH, and the monochlorides, SrCl and BaCl, for red and green. Therefore, as stated above, commonly in red or green pyrotechnics, potassium perchlorate (KClO4) is used—as, a chloride ion and hydroxide ion donor, which also is a strong oxidizer.
One HHS of particular interest is the U.S. Army red signal/illuminating device; the M126A1 parachute. The KClO4-containing in-service M126A1 red signal/illuminating device has a required military specification of a minimum burn time of 50 seconds, a minimum luminous intensity of 10,000 candela, a dominant wavelength of 620±20 nanometers and a minimum spectral purity of 76%. This red military illuminant device is housed within a 10 inch aluminum handheld launch tube, propelled therefrom by a fin stabilized rocket, and floats back to earth suspended from a parachute—providing the desired red illumination or signal as it floats downward. The fin stabilized rocket assembly propels the illuminant device to an altitude of about 700 feet, after which an expelling charge ignites the illuminant and, as stated, the assembly parachutes to the ground.
As stated above, KClO4 acts as an oxidizer, and is so used in the M126A1 illuminant; where, with a second oxidizer, strontium nitrate (Sr(NO3)2), the KClO4 reacts with a 1:1 mixture of magnesium 30/50 and magnesium 50/100, inorganic fuel, to produce magnesium oxide (MgO). MgO is a gray body emitter, and is responsible for producing the necessary illumination intensity desired for the HHS (intensity measured in candela). Further, the reaction of the strontium with the chloride donor from another ingredient, polyvinyl chloride (PVC), to produce strontium (I) chloride (SrCl). SrCl is responsible for imparting the intense red color within the pyrotechnic material, though the strontium reacting with the oxidizer to produce strontium monohydroxide (SrOH) also contributes to the red emission. An organic-basedbinder, usually Laminac/Lupersol, mitigates the sensitivity and prevents separation of the oxidizer, fuel and chloride donor.
Disclosed by Sabatini et al, Propellants, Explosives, Pyrotechnics, Applications of High-Nitrogen Energetics in Pyrotechnics: Development of Perchlorate-Free Red Star M126A1 Hand-Held Signal Formulations with Superior Luminous Intensities and Burn Times, August 2011, Vol. 36, Issue 4, pp. 373-378 (Wiley-VCH Verlag GmbH & Co., KGaA, Weinheim), available online at: http://onlinelibrary.wiley.com/doi/10.1002/prep.201000061/pdf, is an alternative to KClO4 based illuminant formulations for use in HHS, which involves the use of a metal salt, with a strontium core and two nitro groups, i.e. strontium bis-(1-methyl-5-nitriminotetrazolate)monohydrate—a high energy, high nitrogen fuel. While a synthesis of strontium bis-(1-methyl-5-nitriminotetrazolate)monohydrate is disclosed in an article by Thomas M. Klapötke et al., Propellants, Explosives, Pyrotechnics, Coloring Properties of Various High-Nitrogen Compounds in Pyrotechnic Compositions, June 2010, Vol. 35, Issue 3, pp 213-219 (Wiley-VCH Verlag GmbH & Co., KGaA, Weinheim), use of such a synthesis is not amenable to mass, economic production and strontium bis-(1-methyl-5-nitriminotetrazolate)monohydrate is not commercially available.
Clearly there is a need in the art for an inexpensive, commercially available, environmentally friendly, and non-toxic alternative to KClO4 in flare compositions, especially for HHS illuminants.